Time-Lapse Imaging of Cell Death

Ferroptosis-like cell death promotes and prolongs inflammation in Drosophila

Ferroptosis is a distinct form of necrotic cell death caused by overwhelming lipid peroxidation, and emerging evidence indicates a major contribution to organ damage in multiple pathologies. However, ferroptosis has not yet been visualized in vivo due to a lack of specific probes, which has severely limited the study of how the immune system interacts with ferroptotic cells and how this process contributes to inflammation. Consequently, whether ferroptosis has a physiological role has remained a key outstanding question. Here we identify a distinct, ferroptotic-like, necrotic cell death occurring in vivo during wounding of the Drosophila embryo using live imaging. We further demonstrate that macrophages rapidly engage these necrotic cells within the embryo but struggle to engulf them, leading to prolonged, frustrated phagocytosis and frequent corpse disintegration. Conversely, suppression of the ferroptotic programme during wounding delays macrophage recruitment to the injury site, pointing to conflicting roles for ferroptosis during inflammation in vivo.

Automation, live-cell imaging, and endpoint cell viability for prostate cancer drug screens

Androgen deprivation therapy (ADT) is the standard of care for high risk and advanced prostate cancer; however, disease progression from androgen-dependent prostate cancer (ADPC) to lethal and incurable castration-resistant prostate cancer (CRPC) and (in a substantial minority of cases) neuroendocrine prostate cancer (NEPC) is common. Identifying effective targeted therapies is challenging because of acquired resistance to established treatments and the vast heterogeneity of advanced prostate cancer (PC). To streamline the identification of potentially active prostate cancer therapeutics, we have developed an adaptable semi-automated protocol which optimizes cell growth and leverages automation to enhance robustness, reproducibility, and throughput while integrating live-cell imaging and endpoint viability assays to assess drug efficacy in vitro. In this study, culture conditions for 72-hr drug screens in 96-well plates were established for a large, representative panel of human prostate cell lines including: BPH-1 and RWPE-1 (non-tumorigenic), LNCaP and VCaP (ADPC), C4-2B and 22Rv1 (CRPC), DU 145 and PC3 (androgen receptor-null CRPC), and NCI-H660 (NEPC). The cell growth and 72-hr confluence for each cell line was optimized for real-time imaging and endpoint viability assays prior to screening for novel or repurposed drugs as proof of protocol validity. We demonstrated effectiveness and reliability of this pipeline through validation of the established finding that the first-in-class BET and CBP/p300 dual inhibitor EP-31670 is an effective compound in reducing ADPC and CRPC cell growth. In addition, we found that insulin-like growth factor-1 receptor (IGF-1R) inhibitor linsitinib is a potential pharmacological agent against highly lethal and drug-resistant NEPC NCI-H660 cells. This protocol can be employed across other cancer types and represents an adaptable strategy to optimize assay-specific cell growth conditions and simultaneously assess drug efficacy across multiple cell lines.

Dexamethasone sensitizes to ferroptosis by glucocorticoid receptor-induced dipeptidase-1 expression and glutathione depletion

Dexamethasone is widely used as an immunosuppressive therapy and recently as COVID-19 treatment. Here, we demonstrate that dexamethasone sensitizes to ferroptosis, a form of iron-catalyzed necrosis, previously suggested to contribute to diseases such as acute kidney injury, myocardial infarction, and stroke, all of which are triggered by glutathione (GSH) depletion. GSH levels were significantly decreased by dexamethasone. Mechanistically, we identified that dexamethasone up-regulated the GSH metabolism regulating protein dipeptidase-1 (DPEP1) in a glucocorticoid receptor (GR)-dependent manner. DPEP1 knockdown reversed the phenotype of dexamethasone-induced ferroptosis sensitization. Ferroptosis inhibitors, the DPEP1 inhibitor cilastatin, or genetic DPEP1 inactivation reversed the dexamethasone-induced increase in tubular necrosis in freshly isolated renal tubules. Our data indicate that dexamethasone sensitizes to ferroptosis by a GR-mediated increase in DPEP1 expression and GSH depletion. Together, we identified a previously unknown mechanism of glucocorticoid-mediated sensitization to ferroptosis bearing clinical and therapeutic implications.

Membrane-Interacting DNA Nanotubes Induce Cancer Cell Death

DNA nanotechnology offers to build nanoscale structures with defined chemistries to precisely position biomolecules or drugs for selective cell targeting and drug delivery. Owing to the negatively charged nature of DNA, for delivery purposes, DNA is frequently conjugated with hydrophobic moieties, positively charged polymers/peptides and cell surface receptor-recognizing molecules or antibodies. Here, we designed and assembled cholesterol-modified DNA nanotubes to interact with cancer cells and conjugated them with cytochrome c to induce cancer cell apoptosis. By flow cytometry and confocal microscopy, we observed that DNA nanotubes efficiently bound to the plasma membrane as a function of the number of conjugated cholesterol moieties. The complex was taken up by the cells and localized to the endosomal compartment. Cholesterol-modified DNA nanotubes, but not unmodified ones, increased membrane permeability, caspase activation and cell death. Irreversible inhibition of caspase activity with a caspase inhibitor, however, only partially prevented cell death. Cytochrome c-conjugated DNA nanotubes were also efficiently taken up but did not increase the rate of cell death. These results demonstrate that cholesterol-modified DNA nanotubes induce cancer cell death associated with increased cell membrane permeability and are only partially dependent on caspase activity, consistent with a combined form of apoptotic and necrotic cell death. DNA nanotubes may be further developed as primary cytotoxic agents, or drug delivery vehicles, through cholesterol-mediated cellular membrane interactions and uptake.

Detecting retinal cell stress and apoptosis with DARC: Progression from lab to clinic

DARC (Detection of Apoptosing Retinal Cells) is a retinal imaging technology that has been developed within the last 2 decades from basic laboratory science to Phase 2 clinical trials. It uses ANX776 (fluorescently labelled Annexin A5) to identify stressed and apoptotic cells in the living eye. During its development, DARC has undergone biochemistry optimisation, scale-up and GMP manufacture and extensive preclinical evaluation. Initially tested in preclinical glaucoma and optic neuropathy models, it has also been investigated in Alzheimer, Parkinson's and Diabetic models, and used to assess efficacy of therapies. Progression to clinical trials has not been speedy. Intravenous ANX776 has to date been found to be safe and well-tolerated in 129 patients, including 16 from Phase 1 and 113 from Phase 2. Results on glaucoma and AMD patients have been recently published, and suggest DARC with an AI-aided algorithm can be used to predict disease activity. New analyses of DARC in GA prediction are reported here. Although further studies are needed to validate these findings, it appears there is potential of the technology to be used as a biomarker. Much larger clinical studies will be needed before it can be considered as a diagnostic, although the relatively non-invasive nature of the nasal as opposed to intravenous administration would widen its acceptability in the future as a screening tool. This review describes DARC development and its progression into Phase 2 clinical trials from lab-based research. It discusses hypotheses, potential challenges, and regulatory hurdles in translating technology.

Guidelines for Regulated Cell Death Assays: A Systematic Summary, A Categorical Comparison, A Prospective

Over the past few years, the field of regulated cell death continues to expand and novel mechanisms that orchestrate multiple regulated cell death pathways are being unveiled. Meanwhile, researchers are focused on targeting these regulated pathways which are closely associated with various diseases for diagnosis, treatment, and prognosis. However, the complexity of the mechanisms and the difficulties of distinguishing among various regulated types of cell death make it harder to carry out the work and delay its progression. Here, we provide a systematic guideline for the fundamental detection and distinction of the major regulated cell death pathways following morphological, biochemical, and functional perspectives. Moreover, a comprehensive evaluation of different assay methods is critically reviewed, helping researchers to make a reliable selection from among the cell death assays. Also, we highlight the recent events that have demonstrated some novel regulated cell death processes, including newly reported biomarkers (e.g., non-coding RNA, exosomes, and proteins) and detection techniques.

Targeted Prodrug-Based Self-Assembled Nanoparticles for Cancer Therapy

Background

Targeted prodrug has various applications as drug formulation for tumor therapy. Therefore, amphoteric small-molecule prodrug combined with nanoscale characteristics for the self-assembly of the nano-drug delivery system (DDS) is a highly interesting research topic.

Methods and Results

In this study, we developed a prodrug self-assembled nanoplatform, 2-glucosamine-fluorescein-5(6)-isothiocyanate-glutamic acid-paclitaxel (2DA-FITC-PTX NPs) by integration of targeted small molecule and nano-DDS with regular structure and perfect targeting ability. 2-glucosamine (DA) and paclitaxel were conjugated as the targeted ligand and anti-tumor chemotherapy drug by amino acid group. 2-DA molecular structure can enhance the targeting ability of prodrug-based 2DA-FITC-PTX NPs and prolong retention time, thereby reducing the toxicity of normal cell/tissue. The fluorescent dye FITC or near-infrared fluorescent dye ICG in prodrug-based DDS was attractive for in vivo optical imaging to study the behavior of 2DA-FITC-PTX NPs. In vitro and in vivo results proved that 2DA-FITC-PTX NPs exhibited excellent targeting ability, anticancer activity, and weak side effects.

Conclusion

This work demonstrates a new combination of nanomaterials for chemotherapy and may promote prodrug-based DDS clinical applications in the future.

A new protocol for the simultaneous flow cytometric analysis of cytotoxicity and immunotoxicity on zebra mussel (Dreissena polymorpha) hemocytes

Immunotoxicity analysis receives a strong interest in environmental a priori and a posteriori risk assessment procedures considering the direct involvement of the immune system in the health status of organisms, populations and thus ecosystems. The freshwater mussel Dreissena polymorpha is an invasive species widely used in ecotoxicology studies and biomonitoring surveys to evaluate the impacts of contaminants on aquatic fauna. Bivalve hemocytes are the immunocompetent cells circulating in the open circulatory system of the organism. However, there is nowadays no consensus on a protocol to evaluate the immunocompetent state of this particular cell type using flow cytometry. Wild species such as D. polymorpha present several technical barriers complicating their analyze including (i) the quality and the purity of the hemolymph sample, (ii) the controversial characterization of hemocyte subpopulations and their diversity, (iii) the quantity of biological material, and (iv) the high inter-individual variability of hemocyte responses. The present work proposes several technical and analytical improvements to control the above-mentioned issues. The inclusion of sedimentation and cell detachment steps in the pre-analytical phase of the protocol substantially ameliorate the quality of the hemolymph sample as well as the accuracy of the cytometric measurements, by selecting the analyzed cells on their adhesion ability and by increasing the concentration of the analyzed events. The development of an effective triple-labeling procedure including the cellular probe Hoechst® 33342, the membrane impermeant dye propidium iodide and yellow-green fluorescent microspheres allowed the simultaneous analysis of cytotoxicity and phagocytosis activity in hemocytes. It also significantly enhanced the accuracy of hemocyte endpoint measurements by eliminating non-target events from the analysis and allowing relevant gating strategies. Finally, the use of pooled samples of hemolymph noticeably reduced inter-sample variability while providing more plasticity in the experimental design and improving the discriminating potency between treatments. The developed protocol is suitable for ex vivo exposure of hemocyte in a chemical/environmental toxicity assessment as well as for in vivo exposure in the laboratory or in situ biomonitoring surveys with few adaptations.

Genome-wide synthetic lethal CRISPR screen identifies FIS1 as a genetic interactor of ALS-linked C9ORF72

Mutations in the C9ORF72 gene are the most common cause of amyotrophic lateral sclerosis (ALS). Both toxic gain of function and loss of function pathogenic mechanisms have been proposed. Accruing evidence from mouse knockout studies point to a role for C9ORF72 as a regulator of immune function. To provide further insight into its cellular function, we performed a genome-wide synthetic lethal CRISPR screen in human myeloid cells lacking C9ORF72. We discovered a strong synthetic lethal genetic interaction between C9ORF72 and FIS1, which encodes a mitochondrial membrane protein involved in mitochondrial fission and mitophagy. Mass spectrometry experiments revealed that in C9ORF72 knockout cells, FIS1 strongly bound to a class of immune regulators that activate the receptor for advanced glycation end (RAGE) products and trigger inflammatory cascades. These findings present a novel genetic interactor for C9ORF72 and suggest a compensatory role for FIS1 in suppressing inflammatory signaling in the absence of C9ORF72.

Antibody-dependent fragmentation is a newly identified mechanism of cell killing in vivo

The prevailing view is that therapeutic antibodies deplete cells through opsonization and subsequent phagocytosis, complement-dependent lysis or antibody-dependent cellular-cytotoxicity. We used high resolution in vivo imaging to identify a new antibody-dependent cell death pathway where Kupffer cells ripped large fragments off crawling antibody-coated iNKT cells. This antibody-dependent fragmentation process resulted in lethality and depletion of crawling iNKT cells in the liver sinusoids and lung capillaries. iNKT cell depletion was Fcy-receptor dependent and required iNKT cell crawling. Blood, spleen or joint iNKT cells that did not crawl were not depleted. The antibody required high glycosylation for sufficiently strong binding of the iNKT cells to the Fc Receptors on Kupffer cells. Using an acetaminophen overdose model, this approach functionally depleted hepatic iNKT cells and affected the severity of liver injury. This study reveals a new mechanism of antibody-dependent killing in vivo and raises implications for the design of new antibodies for cancer and auto-reactive immune cells.

Acanthamoeba culbertsoni: Electron-Dense Granules in a Highly Virulent Clinical Isolate

The virulence of various amoebic parasites has been correlated with the presence of electron-dense granules (EDGs) in the cytoplasm of trophozoites. Here, we report the finding by transmission electron microscopy of a large number of EDGs in a recent culture of Acanthamoeba culbertsoni, isolated from a severe case of human keratitis. When this isolate was maintained in culture for 6 mo, the granules almost disappeared. However, after induction of mice brain lesions with the long-term cultured isolate, recovered amoebas had abundant EDGs. Trophozoites of the original isolate, or those recovered from experimental lesions, secreted EDGs into the medium when incubated with MDCK cells. To analyze a possible cytotoxic effect the conditioned medium was incubated with MDCK monolayers. After 5 h, the media containing EDGs produced opening of the tight junctions; at 24 h, cell viability was compromised, and at 48 h most of the cells were detached from the monolayer. In contrast, trophozoites in long-term cultures did not release EDGs to the medium during incubation with MDCK cells, and the corresponding conditioned medium did not have any effect on MDCK monolayers. Our observations further support the hypothesis that EDGs play a role in the cytopathogenic mechanisms of A. culbertsoni.

Techniques to Distinguish Apoptosis from Necroptosis

The processes by which cells die are as tightly regulated as those that govern cell growth and proliferation. Recent studies of the molecular pathways that regulate and execute cell death have uncovered a plethora of signaling cascades that lead to distinct modes of cell death, including "apoptosis," "necrosis," "autophagic cell death," and "mitotic catastrophe." Cells can readily switch from one form of death to another; therefore, it is vital to have the ability to monitor the form of death that cells are undergoing. A number of techniques are available that allow the detection of cell death and when combined with either knockdown approaches or inhibitors of specific signaling pathways, such as caspase or RIP kinase pathways, they allow the rapid dissection of divergent cell death pathways. However, techniques that reveal the end point of cell death cannot reconstruct the sequence of events that have led to death; therefore, they need to be complemented with methods that can distinguish all forms of cell death. Apoptotic cells frequently undergo secondary necrosis under in vitro culture conditions; therefore, novel methods relying on high-throughput time-lapse fluorescence video microscopy are necessary to provide temporal resolution to cell death events. Further, visualizing the assembly of multiprotein signaling hubs that can execute apoptosis or necroptosis helps to explore the underlying processes. Here we introduce a suite of techniques that reliably distinguish necrosis from apoptosis and secondary necrosis, and that enable investigation of signaling platforms capable of instructing apoptosis or necroptosis.